Following combat, maintenance and recovery personnel can be exposed to equipment contaminated with depleted uranium. Dust containing depleted uranium can be resuspended during recovery operations, posing an inhalation hazard. Spent depleted uranium rounds and penetrators that were fired but missed their targets may be scattered on the battlefield and can thus potentially lead to additional exposures.
What Happens to It in the Body? After it is ingested, most uranium is excreted from the body within a few days and never enters the bloodstream. The small fraction that is absorbed into the bloodstream (0.2 to 5%) is deposited preferentially in bone and kidneys. Most of what goes to the kidneys leaves within a few days (in urine), while that deposited in bone can remain for many years. After inhalation, generally only a small fraction penetrates to the lung’s alveolar region, where it can remain for years and can also enter the bloodstream.
What Are the Primary Health Effects? Uranium is a health hazard only if it is taken into the body. External gamma exposure is generally not a major concern because uranium emits only a small amount of low-energy gamma radiation, and beta exposure is only of concern for direct handling operations (due to potential skin effects). The main means of exposure are ingestion of food and water containing uranium isotopes and inhalation of uranium-contaminated dust. Ingestion is usually the exposure route of concern unless there is a nearby source of airborne dust. Because uranium is taken up in the body much more readily if inhaled than if ingested, both exposure routes can be important. The major health concern is kidney damage caused by the chemical toxicity of soluble uranium compounds; these effects can be reversible depending on the level of exposure. Uranium is not considered a chemical carcinogen. A second concern is for uranium deposited in bone, which can lead to bone cancer as a result of the ionizing radiation associated with the radioactive decay products. Uranium has caused reproductive problems in laboratory animals and developmental problems in young animals, but it is not known if these problems exist for humans.
What Are the Risks? Lifetime cancer mortality risk coefficients have been calculated for nearly all radionuclides, including uranium (see the companion fact sheet for Uranium). On an activity (curie) basis, these risk coefficients are essentially the same for all three natural uranium isotopes. Hence, the risk is essentially independent of the ratio of the various isotopes in a uranium compound. For this reason, the risk of a fatal cancer from exposure to depleted uranium is essentially the same as for enriched uranium on an activity basis. However, because of the difference in specific activity, equal activities of enriched and depleted uranium have significantly different masses.
The decay of uranium isotopes in depleted uranium results in the generation of radioactive decay products. For example, thorium-234 and protactinium-234m (the “m” meaning metastable) are produced from the decay of uranium-238. The recycling of irradiated uranium may also result in some radioactive impurities in depleted uranium. Some of these decay products and impurities could potentially also exhibit chemical toxicity. The decay products and impurities contribute to the radiation emitted by depleted uranium; however, the concentrations are generally too small to be of significance when assessing the chemical health effects from exposures to depleted uranium.
The extent of chemical damage from exposure to a depleted uranium compound depends on its solubility and the route of exposure. In most assessments, only inhalation and ingestion are considered because although dermal absorption of some soluble compounds (e.g., uranyl nitrate) is possible, these exposures generally are not significant in association with industrial emissions or environmental exposures. When soluble or moderately soluble compounds such as uranyl fluoride (UO2F2) or uranium tetrafluoride (UF4) are inhaled or ingested, some of the uranium enters the bloodstream and reaches the kidney and other internal organs; thus, chemical toxicity is of primary importance.
When insoluble compounds such as UO2 and U3O8 are inhaled, the uranium is generally deposited in the lungs and can remain there for long periods of time (months or years). The main concern from exposure to these insoluble compounds is increased cancer risk from the internal exposure to radioactivity. Ingested insoluble compounds are poorly absorbed from the gastrointestinal tract, and so generally have low toxicity. |
